Medical ultrasound images are typically produced by generating an ultrasonic sound wave traveling in a known direction and observing the echoes created when the sound wave bounces off of boundaries between regions of differing density in the body. For any given direction, the image pixels are generated by plotting a dot whose brightness is proportional to the echo's amplitude at a coordinate whose location is a function of the time after a short pulse is send in the direction in question. The space between the transducer that generates the sound pulse and a strongly reflecting boundary forms a cavity that can reverberate. The resultant images have artifacts that are manifested by a pattern of parallel lines that are typically perpendicular to the direction of incidence of the sound wave.
It would be advantageous to provide an image processing system that can identify and remove these reverberation artifacts. Such a system needs to be able to distinguish the artifacts from the tissue boundary that is providing one wall of the reverberation chamber.
One prior art method for reducing reverberation artifacts utilizes a dual-frequency subtraction technique to suppress such artifacts. This method is based on the observation that echoes corresponding to reverberation artifacts are frequency-independent whereas the diffusely scattered echoes from small scattering centers such a speckle noise are frequency-dependent. Hence, the image obtained by the subtraction of two images at different frequencies has reduced reverberation echoes. Unfortunately, the echoes produced by real boundaries are also removed by this method. Since imaging such boundaries is an important part of ultrasound imaging, this method is less than perfect. Furthermore, the system requires a dual-frequency transducer to obtain the two images at the different frequencies which increase the cost of the system and reduces the frame rate, since two pictures must now be taken and processed for each frame displayed to the operator. Finally, the subtraction is performed in the amplitude domain; hence, care must be taken to match the gains of the two images which further complicates the method.
Broadly, it is the object of the present invention to provide an improved ultrasound imaging system.
It is a further object of the present invention to provide an ultrasound imaging system that can identify and reduce reverberation artifacts.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.